1. Field of the Invention
The present invention relates to an ion-conductive polymer, that is, a polymeric solid electrolyte.
2. Description of the Related Art
Development of organic polymeric solid electrolytes have recently been progressed because of characteristics such as (1) good processing ability and readiness in forming a film having a large area and (2) high flexibility and excellent adhesion to electrodes as compared with inorganic solid electrolytes.
As to the polymeric solid electrolytes, M. B. Armand et al. have proposed mixtures of polyethylene oxide and alkali metal salts in "Fast Ion Transport in Solids", page 131, published from North Hollaud Publishing Co. (1979).
However, preparation of the solid electrolyte is carried out by a so-called casting method where the solid electrolyte is dissolved in a solvent, cast on a molding surface and successively dried by removing the solvent to form a film. Consequently, the processing procedures are complex, the resulting film has a conductivity of 10.sup.-6 S/cm or less at room temperature and the adhesion of the film to the electrodes is also unsatisfactory. Thus the improvement of the film has been strongly desired.
In addition, Japanese Laid-Open Patent 48716 (1987) has disclosed a crosslinking process by reacting trifunctional polyethylene glycol with a diisocyanate derivative. Japanese Laid-Open Patent 285954 (1987) has also disclosed a crosslinking process by polymerization reaction of polyethylene glycol diacrylate. However, solvents are used in any of these processes and a drying step is inevitable for removing the residual solvent after finishing the reaction. Further improvement on the balance of properties including ionic conductivity and adhesion to electrodes has been required. On the other hand, the polymeric solid electrolyte remarkably decreases ionic conductivity in a low temperature region below ordinary temperature. Improvement has also been required on the problem.